RISC-V: Support XVentanaCondOps extension

    Ventana Micro has published the specification for their
    XVentanaCondOps ("conditional ops") extension at
      https://github.com/ventanamicro/ventana-custom-extensions/releases/download/v1.0.0/ventana-custom-extensions-v1.0.0.pdf
    which contains two new instructions
      - vt.maskc
      - vt.maskcn
    that can be used in constructing branchless sequences for
    various conditional-arithmetic, conditional-logical, and
    conditional-select operations.

    To support such vendor-defined instructions in the mainline binutils,
    this change also adds a riscv_supported_vendor_x_ext secondary
    dispatch table (but also keeps the behaviour of allowing any unknow
    X-extension to be specified in addition to the known ones from this
    table).

    As discussed, this change already includes the planned/agreed future
    requirements for X-extensions (which are likely to be captured in the
    riscv-toolchain-conventions repository):
      - a public specification document is available (see above) and is
        referenced from the gas-documentation
      - the naming follows chapter 27 of the RISC-V ISA specification
      - instructions are prefixed by a vendor-prefix (vt for Ventana)
        to ensure that they neither conflict with future standard
        extensions nor clash with other vendors

    bfd/ChangeLog:

            * elfxx-riscv.c (riscv_get_default_ext_version): Add riscv_supported_vendor_x_ext.
            (riscv_multi_subset_supports): Recognize INSN_CLASS_XVENTANACONDOPS.

    gas/ChangeLog:

            * doc/c-riscv.texi: Add section to list custom extensions and
              their documentation URLs.
            * testsuite/gas/riscv/x-ventana-condops.d: New test.
            * testsuite/gas/riscv/x-ventana-condops.s: New test.

    include/ChangeLog:

            * opcode/riscv-opc.h Add vt.maskc and vt.maskcn.
            * opcode/riscv.h (enum riscv_insn_class): Add INSN_CLASS_XVENTANACONDOPS.

    opcodes/ChangeLog:

            * riscv-opc.c: Add vt.maskc and vt.maskcn.

    Series-version: 1
    Series-to: binutils@sourceware.org
    Series-cc: Kito Cheng <kito.cheng@sifive.com>
    Series-cc: Nelson Chu <nelson.chu@sifive.com>
    Series-cc: Greg Favor <gfavor@ventanamicro.com>
    Series-cc: Christoph Muellner <cmuellner@gcc.gnu.org>

3 files changed, 22 insertions, 0 deletions

diff --git a/gas/doc/c-riscv.texi b/gas/doc/c-riscv.texi
index 64fff6a7973..98d5d1bed44 100644
--- a/gas/doc/c-riscv.texi
+++ b/gas/doc/c-riscv.texi
@@ -763,5 +763,11 @@ It is documented in @url{https://github.com/T-head-Semi/thead-extension-spec/rel
 The XTheadSync extension provides instructions for multi-processor synchronization.
 
 It is documented in @url{https://github.com/T-head-Semi/thead-extension-spec/releases/download/2.0.0/xthead-2022-09-05-2.0.0.pdf}.
+@item XVentanaCondOps
+XVentanaCondOps extension provides instructions for branchless
+sequences that perform conditional arithmetic, conditional
+bitwise-logic, and conditional select operations.
+
+It is documented at @url{https://github.com/ventanamicro/ventana-custom-extensions/releases/download/v1.0.0/ventana-custom-extensions-v1.0.0.pdf}.
 
 @end table
diff --git a/gas/testsuite/gas/riscv/x-ventana-condops.d b/gas/testsuite/gas/riscv/x-ventana-condops.d
new file mode 100644
index 00000000000..cab0cc8dc12
--- /dev/null
+++ b/gas/testsuite/gas/riscv/x-ventana-condops.d
@@ -0,0 +1,12 @@
+#as: -march=rv64i_xventanacondops1p0
+#source: x-ventana-condops.s
+#objdump: -d
+
+.*:[ 	]+file format .*
+
+
+Disassembly of section .text:
+
+0+000 <target>:
+[ 	]+0:[ 	]+00c5e57b[ 	]+vt.maskc[ 	]+a0,a1,a2
+[ 	]+4:[ 	]+00e6f57b[ 	]+vt.maskcn[ 	]+a0,a3,a4
diff --git a/gas/testsuite/gas/riscv/x-ventana-condops.s b/gas/testsuite/gas/riscv/x-ventana-condops.s
new file mode 100644
index 00000000000..562cf7384f7
--- /dev/null
+++ b/gas/testsuite/gas/riscv/x-ventana-condops.s
@@ -0,0 +1,4 @@
+target:
+	vt.maskc	a0, a1, a2
+	vt.maskcn	a0, a3, a4
+